The present invention relates to a new and improved construction of a gas-blast switch of the type comprising a fixed contact and a movable contact and a blast or discharge nozzle surrounding one such contact, the inlet of the blast nozzle being connected at the outlet of a pump compartment for an extinguishing gas, this pump compartment can be placed under pressure or pressurized by the switch cut-off or switching-off movement, and further, wherein the narrowest location or throat of the blast nozzle is arranged downstream of the blowing direction of the extinguishing gas with respect to the aforesaid one contact, and the outlet of the pump compartment can be closed by means of a check or nonreturn valve which closes in the direction of the pump compartment.
During the course of switching-off such type switch there prevails, as is well known, an arc. The intensity of this arc is dependent upon the momentary value of the current. Owing to its high temperature the arc, as a function of its intensity, heats-up the extinguishing or quenching gas delivered thereto from the pump compartment and which gas blows against the arc. Consequently, there prevails a pressure surge which counteracts the blowing pressure emanating from the pump compartment and forces back the extinguishing gas expelled therefrom. This counter pressure causes the check valve which is associated with the outlet of the pump compartment to close such outlet. As a result, there is prevented the penetration of the arc gases into the pump compartment, and which arc gases at that moment in time are still hot and as a general rule ionized and contaminated with metallic vapors. This enables at the same time reducing the power requirements for the switch drive, because such of course not only is responsible for the switching-off or cut-off movement of the movable contact, rather also must bring about the compression of the extinguishing or quenching gas in the pump compartment.
While with this arrangement there is present the advantage which is derived from the provision of the check valve operatively associated with the outlet of the pump compartment, there is also, however, present the disadvantage that the arc as a practical matter no longer can be blown for such length of time as the pressure of the arc gases exceed the pressure prevailing in the pump compartment -- it being mentioned that the pressure of the arc gases does however decrease with the decreasing current and the pressure in the pump compartment increases as the switching-off or cut-off movement progresses-- i.e. as long as the check valve is closed.
In other words, with the state-of-the-art switches of the previously mentioned type there cannot be achieved, or at least not to a sufficient degree, a blowing of the arc just at that time span when the blowing action would be most effective in consideration of the subsequent null-crossover of the current. In any event, the heretofore known prior art switches of the previously mentioned type do not even approximately permit of a current-dependent blowing of the arc.